Alzheimer's disease (AD) is characterized by deposition of amyloid beta (A?), gliosis, and extensive neuronal loss. However, most commonly studied AD mouse models focus on plaque pathology, and do not exhibit neurodegeneration. Importantly, it is unknown if neuronal death is a consequence of amyloid pathology or reactive gliosis. We will utilize the Vassar 5XFAD mouse model to determine if neuronal death is principally caused by accumulation of intraneuronal amyloid precursor protein (APP) or by subsequent reactive gliosis with the overarching goal of validating the therapeutic potential of RXR agonist Bexarotene (Bex). As an RXR agonist, Bex affects multiple cell types (i.e neurons, microglia, and astrocytes) and may induce a variety of unexplored downstream effects including authophagy. We have chosen a mouse model well suited for studying neuronal death, the 5XFAD. 5XFAD amyloid beta deposition originates in neurons around 1-2 months of age, cognitive deficits are detected at 4 months, and considerable neuronal death is observed at 8 months with abundant gliosis throughout. Cramer et al demonstrated the role of RXR nuclear receptor signaling and ApoE in reducing amyloid pathology and improving cognition in several non-degenerative AD mouse models. Bex induces the transcription of cholesterol metabolism genes ApoE, Abca1, and Abcg1, and conversely down regulates proinflammatory gene expression. Preliminary data was obtained using 4 and 8 month 5XFAD mice which received 7 day Bex treatment. Bex treatment in 5XFAD mice increased ApoE, Abca1, and Abcg1 levels and reduced soluble and insoluble amyloid species. Importantly, intraneuronal APP/ A? was significantly reduced in cortical layers V and IV in 4 month 5XFAD mice. This correlated to 8 month 5XFAD improvements in olfaction behavior after 7 day Bex. Furthermore, Bex treatment increased association of microglia with amyloid plaques. Therefore, we hypothesize that long term Bex treatment in 5XFAD mice can prevent or attenuate neuronal death at later ages through reduction in soluble A? and suppression of gliosis. Autophagy is an attractive mechanism for Bex removal of APP/ A?, since defects in autophagy have been implicated in several diseases of protein misfolding and neurodegeneration including AD. Furthermore, preliminary western analysis has indicated that Bex treatment alters protein expression of Beclin-1 and LC3II which are critical for initiation of autophagy and autophagosome formation, respectively. Our preliminary data indicates Bex decreases intraneuronal APP. Defining the mechanism of APP removal is critical for fully understanding and interpreting Bex treatment. RXR and PPAR heterodimers also reduce inflammatory gene expression through suppression of NFkB. The regulation of NFkB is most critical for the proinflammatory activation of microglia, the main immune effector cell of the brain. Microglia respond to A? by induction of NFkB driven gene expression and production of neurotoxic inflammatory mediators (i.e. TNF , IL-6, and IL-1) and inhibition of phagocytosis of A?. In vitro studies have established that both LXR and PPAR- agonists downregulate inflammatory gene expression in microglia, though the effects of RXR agonist, Bex, on microglia has not been quantified. However, it is unknown whether neuronal death can be attributed to amyloid beta aggregates or the subsequent inflammatory responses. Collectively, these aims will provide critical insight into the relative contributions o intraneuronal APP and reactive gliosis to neuronal death and whether Bex can ameliorate both pathologies through diverse mechanisms.